Observations of the Cochlear Blood Circulation in. Guinea Pigs by the Impedance Plethysmography

Abstract

The author observed the cochlear blood circulation in the slightly anesthetized guinea pigs by means of the impedance plethysmography. This method is based upon the principle that changes in the blood volume in a given part cause changes in electrical impedance in the same portion(Fig. 1).
Two electrodes were inserted carefully into the basal turn of the cochlea 2 to 3mm. apart with a microboring machine and fixed by dental cement(Fig. 2).
Thus the changs of the cochlear circulation of the living guinea pigs in the physiological and pharmacological respects were observed.
All drugs were given intravenously through a polyethylen tube inserted into a jugular vein.
The results obtained are as follows
1. By the occlusion of an artery, the amplitude of the puls wave at the peripheral small artery decreased parallel to the degree of the occlusion(Fig. 3).
The increase of the amplitude means an increase in the blood flow and conversely a decrease of it means a decreas in blood flow at the given part.
2. The cochlear blood flow was very stable and constant under normal physiological circumstances.
3. Anoxia caused a marked increase of the amplitude, but it abruptly decreased in 30 sec. to 2 min. and became almost unnoticeable. By the resumption of respiration, the amplitude completely recovered and schowed a remarkable increase without an artificial respiration.(Fig. 4 a, b).
The breathnig of a high concentrate 02 caused a decrease of the amplitude, namely the cochlear blood flow(Fig. 4c).
The breathing of a mixture of 10% CO2 in oxygen caused a marked increase of the amplitude under an artificial respiration(Fig. 4d).
4. Alkalosis, produced by the infusion of 10cc/kg of 7 % sodium bicarbonate solution, markedly increased the amplitude of the pulse wave and respiratory wave, continuing about 10min.
Acidosis, produced by the infusion of 4cc/kg of 0.8% ammonium chloride solution, tem-porarily decreased the amplitude. But the very increase was sometimes observable contrary to the expectation(Fig. 5 a, b).
5. Adrenaline, in dose of 0.01mg/kg, caused a decrease during the first few seconds, and then a remarkable increase of the amplitude, but in 2 to 3 min. later, the amplitude again decreased. Noradrenaline, in a dose of 0.2mg/kg, also caused a decrease at first and then an increase, but no subsequent decrease.
The difference seems to come from the difference in dosage(Fig. 6a, b).
6. Acetylcholine, in a dose of 0.001mg/kg, temporarily increased the amplitude(Fig. 7).
7. Pilocarpine, in a dose of 0.1mg/kg, caused a demonstrable increase of the amplitude and simultaneously a decrease of the pulse frequency. But the recovery in frequency could be transiently observed, therefore the author concluded that pilocarpin dilated the cochlear blood vessels and initially decreased, subsequently increased the cochlear blood flow(Fig. 8).
8. Atropine, in a dose of 0.2mg/kg, caused a slight decrease of the amplitude, namely the cochlear blood flow(Fig. 9).
9. Imidaline(Priscol), in a dose of 1mg/kg, caused at first a decrease, and in about 1 min. a considerable increase of the amplitude, which continued about 6min(Fig. 10).
10. Papaverine, in a dose of 1mg/kg, caused a dramatic increase of the amplitude continuing about 6 min.
Papaverine was the most effective drug to the cochlear blood vessel in these experiments.(Fig. 11).
11. It is noteworthy that nicotinic acid, in a dose of 10mg/kg, did not cause any change in the amplitude but decreased clearly the pulse frequency. Therefore, the author concluded that nicotinic acid did not increase the cochlear blood flow (Fig. 12).
12. Kallikrein, in a dose of 0.1u/kg, also dis not cause any change in the amplitude(Fig. 13).
13. Amylnitrate, inhaled about 20 sec, caused a marked increase in the amplitude(Fig. 14).